1. Field of the Invention
This invention relates to a composition containing stabilized furfural or glycol esters of a vegetable oil fatty acid and an antioxidant such as butylated hydroxy toluene. Such a composition is useful, for example, as an additive in latex film-forming compositions. This invention also relates to latex film-forming compositions containing a stabilized furfural or glycol ester. This invention is also directed to methods of stabilizing furfural or glycol esters of a vegetable oil fatty acid by contacting the ester with an antioxidant such as butylated hydroxy toluene. This invention also includes methods of preparing film-forming compositions comprising the stabilized furfural or glycol esters such as the stabilized PGME mixtures disclosed herein.
2. Related Art
A coating composition is generally film-forming. “Film-forming”, as used herein, means that the coating composition has a minimum Film Forming Temperature (MFT) at, or below, the ambient temperature, to allow for fusion of the polymer into a continuous film. Volatile organic compounds (VOCs), such as coalescents, can be used to temporarily lower the MFT of a coating composition, allowing the polymer to form a film at a temperature below the glass transition temperature (Tg) of that polymer.
Water-based latex paint is comprised of an aqueous dispersion of pigments and latex particles that impart substrate hide, water resistance, and durability to the solid paint film. Other components such as dispersants, surfactants, and thickeners are added to the liquid paint to maintain a stable dispersion and suspension of the pigments and latex particles. Solvents, bases, defoamers, and biocides are also incorporated to improve liquid stability, application performance and film formation properties. The chemical composition of water-base latex paints is designed to allow dispersion of components in water, yet maintain water resistance upon curing and forming a dry paint film. Essentially, the compositions are designed to contain a hydrophobic component for water resistance as a paint film, and a hydrophilic component to improve stability, solubility, and dispersion in the liquid aqueous phase.
A latex polymer is a high molecular weight component which imparts water resistance and durability to the dry paint film. These latex polymers include polymerization and co-polymerization products of: vinyl acetate, acrylic acid, methacrylic acid, styrene, alpha-methyl styrene, butadiene, acrylates, methacrylates, vinyl chloride, vinylidene chloride and acrylonitrile containing monomers. Particularly important are polymers and co-polymers of alkyl acrylates, alkyl methacrylates, styrene, and vinyl acetate.
Latex polymers are the film-forming portions of the paint film, and are prepared by an emulsion polymerization reaction. Aggregation of polymer particles is typically discouraged by including a stabilizing surfactant in the polymerization mix. In general, the growing latex particles are stabilized during emulsion polymerization by one or more surfactants such as an anionic or nonionic surfactant, or a mixture thereof, as is well known in the polymerization art. Many examples of surfactants suitable for emulsion polymerization are given in McCutcheon's Detergents and Emulsifiers (MC Publishing Co., Glen Rock, N.J.), published annually. Generally, emulsion polymerization consists of using nonionic surfactants to create monomer micelles within the water phase.
The effectiveness of the latex polymer in forming a film after the paint has been deposited upon a surface depends upon the Tg of the polymer and the temperature at which the paint film is allowed to dry. Coalescing aids, compounds compatible with the polymer, have been used in latex paints to plasticize (soften) the latex polymer to allow the formation of a continuous film with optimum coating properties once the water has evaporated. Without the coalescing aid, the coatings may crack and fail to adhere to the substrate when dry. Traditionally, such coalescing aids (generally alcohol esters and ethers) are volatile and leave the film after they have enabled the polymer to coalesce into an integral film. Once the coalescing aids are gone, the original hardness of the polymer, defined by its initial Tg, returns yielding a tougher and more resistant coating.
One problem encountered by the coatings manufacturers is the development of formulations containing low VOC-coalescing aids or plasticizers. For instance, emulsion polymers are currently formulated with coalescing aids or plasticizers in order to form films at and below ambient conditions yet dry to films of sufficient Tg to perform adequately at and above room temperature. In general, the ability of emulsion polymers to form or coalesce into film is governed by the MFT of the polymer in question, which typically approximates Tg of that polymer. Thus, there is a dilemma, i.e., low MFT polymers are required in order to exhibit coalescence, flow, and surface wetting properties. However, if the polymer remains soft and tacky, the coatings are not usable. Therefore, it is necessary to develop a technology in which coating formulations contain suitable ingredients with an initial low MFT, followed upon application forms nontacky, durable, hard, and water resistant surfaces having a Tg significantly above their MFT.
In contrast to latex compositions, oil-based compositions, e.g., oil-based paints, commonly employ vegetable oils such as linseed oil or tung oil and/or vegetable oil co-reacted with other compounds (such as alkyd resins) as a component of the vehicle in the paint. The vegetable oils, which are also referred to in the art as “drying oils”, form crosslinked films upon exposure to air. Like all vegetable oils, these drying oils are triesters of various fatty acids and glycerol. However, unlike most vegetable oils, the fatty acids in drying oils have a very high degree of unsaturation (high iodine value), are high in polyunsaturated fatty acids, and generally have a majority of fatty acids that contain 3 or more double bonds (such as linolenic [cis-9-cis-12-cis-15-Octadecatrienoic] acid, eleostearic [cis-9-trans-11-trans-13-Octadecatrienoic] acid, and 4-Oxo-cis-9-trans-11-trans-13-Octadecatrienoic acid). Semi-drying oils have moderate to high degrees of unsaturation, and are high in polyunsaturated fatty acids, but contain lower levels of fatty acids that have 3 or more double bonds. The use of such reactive drying oils in oil based paints helps to provide a paint film which is hard and durable. Thus, the drying oils and co-reacted vegetable oil products (alkyds) are desirable components of oil-based compositions. However, oil based compositions typically comprise large proportions of VOCs as solvents or additives, e.g., 380 to 450 grams per liter (g/l) or more. Such high concentrations of VOCs are environmentally undesirable.
Latex compositions, on the other hand, typically comprise very low concentrations of VOCs, e.g. less than about 250 g/l, and thus are more environmentally compatible. Accordingly, it would be desirable to incorporate the drying oils of oil-based compositions into latex compositions to promote crosslinking of the latex compositions. However, the drying oils used in oil-based compositions are not water-soluble and accordingly cannot readily be used in latex compositions.
A latex or emulsion composition containing drying oils is disclosed in U.S. Pat. Nos. 6,203,720 and 6,174,948. The compositions disclosed in these patents contain crosslinkable monomers having a fatty acid residue derived from semi-drying or non-drying oils and chemically attached to ethylenically unsaturated carboxylic acids. The monomers are polymerized to yield a latex polymer resin with oxidative cross-linking capability.
It is desirable to develop a latex paint formulation which incorporates components that can react during the curing process, and thereby help form a durable, water-resistant paint film. It is also desirable to reduce the amounts of VOCs, such as coalescing solvents, which are environmentally undesirable.
PGME mixtures can be used to replace traditional coalescing solvents such as 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate (Trade name: Texanol) (N. Jiratumnukul and M. R. Van De Mark, J. Am. Oil. Chem. Soc., 2000, 77, 691-697). Traditional coalescing solvents are VOCs. Thus, it is desirable to minimize the use of these solvents or replace them entirely with non-volatile compounds. PGME mixtures behave as coalescing solvents, but such PGMEs are non-volatile. Thus, PGME remains in the dried film.
The yellowing of dried films containing PGME has been attributed to the presence of PGME in the dried film. Further, in these paints, in-can yellowing is also attributed to the presence of PGME. It is desirable to formulate a latex film-forming composition that contains PGME mixtures as coalescing solvents but exhibit yellowing similar to coatings containing traditional coalescing solvents.